1. Field of the Invention
The present invention relates to a liquid electrophotographic printer, and more particularly, to a squeegee roller driving apparatus for squeegeeing excess developer liquid from a transfer surface of a photosensitive medium.
2. Description of the Related Art
As shown in FIG. 1, a liquid electrophotographic printer such as a color laser printer includes a development device 20 for supplying a developer liquid to an electrostatic latent image formed on a transfer surface 10a of a photoreceptor belt 10 as a photosensitive medium to develop the electrostatic latent image.
In the development device 20, a developer liquid spray nozzle 21, a development roller 22 and a squeegee roller 23 are sequentially installed. The development roller 22 transfers a developer liquid to the transfer surface 10a of the photoreceptor belt 10. The squeegee roller 23 squeezes the developer liquid transferred on the transfer surface 10a of the photoreceptor belt 10. Reference numerals 12 and 13 denote backup rollers opposite to the development roller 22 and the squeegee roller 23 to apply tension to the photoreceptor belt 10.
The development roller 22 and the squeegee roller 23, as shown in FIG. 2, are installed in separate elevation apparatuses 32 and 33, respectively to be controlled to elevate according to the operating mode of the printer. Although not shown in detail, generally the elevation apparatuses 32 and 33 each includes a spring (not shown) configured to adjust its elastic force by a cam mechanism (not shown). In response to the adjusted elastic force of the spring, the development roller 22 and the squeegee roller 23 are lifted or lowered to be engaged in proximity of or disengaged away from to the photoreceptor belt 10.
In the case where the printer is in a printing mode, the development roller 22 and the squeegee roller 23 remain in a lifted state by the driving of the elevation apparatuses 32 and 33. Here, the development roller 22 is lifted up to a location at which a gap of about 0.1 to 0.2 mm is formed between the photoreceptor belt 10 and the development roller 22. The squeegee roller 22 is lifted up to a location at which it presses the photoreceptor belt 10 with a force of approximately 20 kilograms even after it contacts the photoreceptor belt 10. In the case where the printer is in a stop mode, the development roller 22 and the squeegee roller 23 are lowered to be completely disengaged from the photoreceptor belt 10.
As the printing operation is carried out, the developer liquid may accumulate and remain on a contact portion of the squeegee roller 23 and the photoreceptor belt 10. The excess developer liquid remaining on the photoreceptor belt 10 is referred to as a drip line (D). In order to obtain a clean-quality printed image, it is necessary to remove the drip line D at regular time intervals during the printing operation.
FIG. 2 illustrates the positional relationship between the photoreceptor belt 10, the development roller 22 and the squeegee roller 23 in a drip line removal mode, in which the development roller 22 is completely disengaged from the photoreceptor belt 10, as in the stop mode. Also, the squeegee roller 23 is controlled to rotate in reverse with respect to the rotating direction of the photoreceptor belt 10 in the printing mode, while the photoreceptor 10 remains pressed with a loading force of approximately 2 kilograms by adjusting the elastic force of the spring provided in the elevation apparatus 23.
As shown in FIG. 3, a conventional driving apparatus for rotating the squeegee roller 23 in reverse with respect to the traveling direction of the photoreceptor belt 10 includes a squeegee gear 24 installed at a shaft end of the squeegee roller 23, and a driving gear 25 installed at an output end of a driving source (M) positioned above the squeegee gear 24 to be engaged therewith.
In general, the squeegee roller 23 is configured to be capable of rotating in a forward or reverse direction, by installing a one-way bearing or clutch (not shown) on the driving shaft of the driving gear 25. In other words, the squeegee roller 23 contacts the photoreceptor belt 10 in the printing mode to rotate in the same direction as that of the photoreceptor belt 10 (in a forward direction) due to a frictional force therebetween. In a drip line removal mode, the squeegee gear 24 is subjected to the driving force applied from the driving gear 25 to rotate reversely.
According to the above-described conventional squeegee roller driving apparatus, in the course of switching from a drip line removal mode, as shown in FIG. 4A, to a stop mode, as shown in FIG. 4B, the squeegee roller 23 is lowered so that the driving gear 25 and the squeegee gear 24 are spaced apart from each other, thereby stopping rotation. In this case, since the squeegee roller 23 stops temporarily on the transfer surface of the photoreceptor belt 10, the drip line D is not completely removed due to the rolling trace of the squeegee roller 23, leaving a small amount of carrier (approximately 0.005 gram) on the transfer surface of the photoreceptor belt 10. As shown in FIG. 5, the remaining carrier is transferred to an image (D') on printing paper 1, degrading the print quality of the printed image.